dubstepped: "Why only those things and not something else?"
Natural selection is the answer. There has been many, many "something elses", they are only good enough to last one or few generations.
I will give you my understanding in a nutshell. For me evolution is essentially constant change, especially In our DNA (mutations). It's almost like dropping a bunch of coins on the floor repeatedly. You are bound to see every time a different distribution of coins. That's because it's practically impossible to replicate the conditions of the event every time. In the case of evolution also every time that there's a new generation is bound to be different from the previous one, but it becomes increasingly noticeable because, unlike coins, life multiplies. So from this practical observation, it's rather easy for to accept, even be fascinated, by a simple fact of life; the only constant is change itself.